I'm sorry but I have not done this...yet. Don't even have a replacement microphone in hand yet.

But I would expect that the "polarity" of the microphone would not make any difference, unless it requires DC power. But I guess it is possible it is some kind of powered microphone. The way to test that would be to apply a DC voltmeter across the two leads that attach to the microphone while the iphone is powered on (and maybe while the microphone is accepting input). Of course if it is powered this tells you it has a polarity, but not which way to install it.

Does the new microphone appear asymmetrical to you?